Bad EGR valve or EGR solenoid?

[Robotaz]

My car was missing the vac line from the EGR valve to the EGR solenoid. In this configuration the engine light comes on out on the highway and stays on. When I connect it, the car sputters at idle and the light comes on during most driving, but goes off when I accelerate half throttle or more. Which of the two parts do yall think is bad, if either? Too bad I don't know how they work!